All cellular handsets have to be calibrated and tested during production in order to tune them and verify that they behave according to defined requirements. With the technology used presently in production, these activities take a substantial time to process, and high costs are related to this production time. Furthermore, the trend is to add more Radio Access Technologies (RATs) and frequency bands into the same produced unit, and this will drive test and calibration time to even higher numbers.
One large contributor to test time is verification of the receiver quality. Present technology normally uses either standard connected calls or simplified connected calls, where the tested unit, or device under test (DUT), is set to receive and decode information on a specific communication channel under a specific static radio environment. The quality of the decoded information, normally quantified as bit error rate (BER) or throughput, is used as a quality value of the receiver. Another quality verification method used by some manufacturers is to use a simple non-modulated signal as an input signal and a signal-to-noise-ratio (SNR) estimate of the received (output) signal as a quality value.
U.S. Pat. No. 7,203,472 to Seppinen et al., for example, states that it discloses, among other things, a method of operating a radio frequency (RF) that includes generating a calibration signal; injecting the calibration signal after any antenna into a low noise amplifier (LNA) of the RF receiver; and measuring a frequency down-converted response of the receiver at a plurality of different frequencies of the calibration signal.
U.S. Pat. No. 5,737,693 to Aldridge et al. is an example of a baseband simulation system for testing an RF subsystem of a communication device under test. In a transmit mode, pre-stored discrete in-phase (I) and quadrature (Q) samples are retrieved from which transmit analog I and Q signals are reconstructed and provided to the RF subsystem under test to determine the ability of the RF subsystem under test to modulate the analog I and Q signals onto one or more RF carrier signals. In a receive mode, analog I and Q signals received from the RF subsystem are converted to I and Q samples that are analyzed to determine the ability of the RF subsystem under test to demodulate the RF carrier signals to output the analog I and Q signals.
U.S. Patent Application Publication No. US 2005/0260962 by Nazrul et al. describes a test system that emulates the analog processing portion of a communication device and adjusts input signals based on distortions specified by a user and control signals generated by a baseband processing portion of the communication device. It appears that the test system does not measure receiver quality.
GB2439769 by Dubois et al. describes a device for testing a baseband part of a first transceiver (e.g., a mobile phone) that simulates the baseband of a second transceiver (e.g., a base station), and a device for testing a front-end part of the first transceiver that simulates the baseband of the first transceiver and baseband and front-end of the second transceiver.
Current quality verification technology using the receiver decoder prior to quality detection has several problems. For example, receivers need to decode information correctly and so the acceptable error thresholds on decoded information are very low. To get a statistically relevant quality measure, a lot of information has to be received. This typically leads to long quality-measurement times, typically about one second for a single measurement.
For another example, modern decoding techniques are very good at correcting errors. This leads to a very sharp transition between detecting a DUT as good and detecting the DUT as bad. The actual position of the transition is very difficult to estimate from a single measurement under a specific radio condition. The conventional test shows only that a DUT either passes or fails under the test condition; it does not estimate at all under what conditions the DUT will fail.
In addition, since decoders are very good at correcting errors and radio test conditions in factories are very simple static tests with no multipath conditions, there is a non-negligible probability that actual errors in a DUT will not be detected by a test. Moreover, using a DUT's decoder forces the DUT to involve fairly complex signaling or semi-signaling scenarios with extra cost in test time as well as added requirements on the test signal generator and other equipment.
Furthermore, current receiver quality verification techniques focus mainly on verifying performance in situations where noise is the dominant disturbance. These tests are typically relevant to verifying that a DUT is able to receive weak signals close to radio-cell boundaries. That is, however, not such a dominant scenario any more. With the introduction of wireless broadband communication, it has become important for a DUT to have low enough distortion to enable high speed communication. Distortion can be tested using quality measurements after a DUT's decoder, but that is normally not done due to the extra time required in production. Quality verification methods that estimate the SNR of a non-modulated carrier also cannot be used for distortion verification because the test signal needs to be modulated with a statistically relevant signal to enable distortion quality measurement.